This invention relates to a rotor for an electric rotary machine having an inductor provided on a periphery thereof to generate signals for detecting a rotational angle position and/or a rotational speed of a rotary shaft and more particularly to a rotor for an electric rotary machine suitably used to generate signals for supplying an information on a crank angle of an internal combustion engine or an information on a rotational speed thereof to an ignition system and/or a fuel injection system of the engine.
There are required signals containing the engine crank angle information and the rotational speed information for controlling an ignition timing in the ignition system and the fuel injection system for the internal combustion engine. In many cases, there has been used a signal generation device comprising an inductor type rotor mounted on a crankshaft of the engine and a signal generator to generate pulse signals by detecting edges of magnetic poles of the inductor of the rotor in order to obtain the crank angle information and the rotational speed information.
For some motors such as a brushless DC motor, an inductor type signal generation device has been used in case that the information on the rotational angle of the rotary shaft and on the rotational speed thereof are required.
As well known, the inductor type rotor comprises a rotor yoke formed of ferromagnetic material such as iron and/or the like and, on a periphery of the rotor yoke, inductor magnetic poles which may be of a protrusion or a recess are provided.
The signal generator to generate the pulse signals by detecting the edges of the inductor magnetic poles comprises an iron core having a magnetic pole provided at its leading end so as to be faced to the inductor magnetic poles, a signal coil wound on the iron core and a permanent magnet magnetically bonded to the iron core. The signal generator induces the pulse signals at the signal coil due to variation in magnetic flux flowing through the iron core when the forward edge of the inductor magnetic poles as viewed in the rotational direction begins to be faced to the magnetic pole of the iron core on which the signal coil is wound and when the rearward edge of the inductor magnetic poles ends to be faced to the magnetic pole of the signal generator.
In some cases, the rotor yoke of the inductor type rotor is exclusively provided for the signal generation device, but in case that the rotor of the magneto generator is mounted on the crankshaft of the internal combustion engine, the rotor yoke of the magneto generator is commonly used for the rotor yoke of the inductor type rotor.
In some signal generation devices for obtaining the information on the rotational angle of the rotary shaft of the motor having an outer rotor, the rotor yoke of the motor may be commonly used for the rotor yoke of the signal generation devices.
The rotor yoke of the electric rotary machine such as the magneto generator or the outer rotor type motor comprises a cup-like member having a cylindrical peripheral wall and a bottom wall provided so as to close one axial end of the peripheral wall and a boss provided on a central portion of the bottom wall is mounted on the crankshaft of the engine. On an inner surface of the peripheral wall of the rotor yoke, a permanent magnet is mounted, for example, which forms a magnetic field system of the rotor.
In an inner side of the rotor, an armature comprising an armature core and an armature coil wound on the armature core is disposed, and the electric rotary machine is formed by the armature and the rotor.
In case that the rotor yoke of the electric rotary machine such as the magneto generator or the motor is commonly used for the rotor yoke of the signal generation device, the inductor magnetic poles of projections or recesses are provided on the outer surface of the peripheral wall of the rotor yoke.
In the conventional rotor having the inductor magnetic poles provided on the outer periphery thereof, the inductor magnetic poles are directly formed on the outer surface of the peripheral wall of the rotor yoke, or a ring-like inductor forming member having the inductor magnetic poles provided on its outer surface is fixed to the outer surface of the rotor yoke by shrinkage fit.
In case that the inductor magnetic poles are directly formed on the outer surface of the peripheral wall of the rotor yoke of the electric rotary machine, the inductor magnetic poles may be formed by embossing portions of the peripheral wall of the rotor yoke in an outwardly radial direction. However, with the inductor magnetic poles formed by embossing the portions of the peripheral wall of the rotor yoke in this manner, the peripheral wall of the rotor yoke disadvantageously tends to have much strain applied thereto because force is locally applied to the peripheral wall of the rotor yoke when it is embossed, especially if it has many inductor magnetic poles.
It will be considered that the inductor magnetic poles may be formed by cutting the outer periphery of the rotor yoke, but this is inevitably expensive.
In order to avoid this, it has been tried to mount the inductor forming member having the ring-like portion and the inductor magnetic poles formed on the outer surface of the ring-like portion on the outer surface of the peripheral wall of the rotor yoke by shrinkage fit. However, if the shrinkage fit is loose, the inductor forming member is shifted relative to the rotor yoke so that the phase of the signals generated by the signal generation device is also shifted, which disadvantageously fails to obtain the accurate rotational angle information from the signal. Thus, in case that the inductor forming member is mounted by shrinkage fit, it should be severely managed, but this requires more steps for the management of the precision in size when the inductor forming member and the rotor yoke are manufactured and therefore this cannot avoid high cost.
Furthermore, because higher force is applied to the peripheral wall of the rotor yoke when the inductor forming member is fixed to the rotor yoke by shrinkage fit, the strain in the peripheral wall of the rotor yoke disadvantageously gets higher as it is thinner.
Accordingly, it is a principal object of the invention to provide a rotor for an electric rotary machine in which a ring-like inductor forming member can be mounted on a periphery of a rotor yoke without any large strain in a peripheral wall of the rotor yoke.
It is another object of the invention to provide a rotor for an electric rotary machine in which inductor magnetic poles can be formed on a periphery of a rotor yoke without any troublesome process such as cutting and without any shrinkage fit which requires a troublesome management of manufacturing steps.
It is further object of the invention to provide a rotor for an electric rotary machine in which an inductor forming member can be positively positioned on and fixed to a periphery of a rotor yoke so that the inductor magnetic poles are never shifted relative to the rotor yoke.
In accordance with one aspect of the present invention, there is provided a rotor for an electric rotary machine comprising; a rotor yoke having a cylindrical peripheral wall and a bottom wall provided integrally with the peripheral wall so as to close one axial end of the peripheral wall and having a boss provided at a central portion of the bottom wall for mounting a rotary shaft; an inductor forming member having a ring-like portion and inductor magnetic poles formed on an outer surface of the ring-like portion, the ring-like portion fitted onto an outer surface of the rotor yoke; and the inductor forming member being fixed to the rotor yoke by forcing protrusions formed on the peripheral wall of the rotor yoke against both of axial ends of the ring-like portion.
The protrusions may be formed by embossing portions of the peripheral wall of the rotor yoke. Although this requires embossing process, the embossed protrusions are required to have just the number necessary for fixing the inductor forming members and not required to have the number corresponding to the number of the inductor magnetic poles. Thus it will be noted that, in case that many inductor magnetic poles are provided, the rotor yoke never has high strain even though the protrusions are formed by embossing.
In a preferred form, the peripheral wall of the rotor yoke may have a plural of protrusions formed on an outer surface thereof by embossing, which includes a first protrusion portion extending in an axial direction of the rotor yoke and a second protrusion portion extending in a circumferential direction of the rotor yoke. In this case, the inductor forming member may have recesses on an inner surface of the ring-like portion and the inductor forming member is positively positioned in the circumferential direction by engaging the first protrusion portions with the recesses. The inductor forming member is positively positioned on the rotor yoke in the axial direction by forcing the second protrusion portion of each of the protrusions against one of the axial ends of the ring-like portion of the inductor member and by forcing a projection formed by raising the end of the first protrusion portion against the other end of the ring-like portion.
With the rotor constructed in this manner, since the inductor forming member can be positively positioned not only in the circumferential direction, but also in the axial direction relative to the rotor yoke, there can be obtained the rotor for the electric rotary machine which never fails to shift the position of the inductor.
In another preferred form, the plural of protrusions extending in the axial direction may be formed on the outer periphery of the rotor yoke by embossing, and the inductor forming member may be positioned in the circumferential direction by engaging each of the protrusions with recesses provided in an inner surface of the ring-like portion of the inductor forming member. The inductor forming member may be positioned in the axial direction by forcing the protrusion portions formed by raising both ends of each of the protrusions against both axial ends of the ring-like portion of the inductor forming member.